*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}
.header{
    width: 700px;
    margin: auto;
    margin-top: 100px;
    margin-left: 500px;
}
.header ul li{
    display: inline-block;
}
.header div{
    display: inline-block;
}
.bo div{
    display: none;
}
.bo .obo{
    display: block;
}
.header .box .box1{
    font-weight: bold;
    border-bottom: 2px solid #000;
}
.header .box .box1:hover{
    color: aqua;
}